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Jim Krause | Classes | P354 Program Graphics & Animation

Week 12


  • Final Project proposals are due Thursday. Final Project scripts/storyboards due next week


  • Review homework
  • Motion tracking (continued)
  • Keying (Thursday)

Useful AE resources:

Review homework

Multipart Tracking Exercise (5 points)

In this exercise, you'll show you can track an object, even though it moves out of the frame or is blocked. You'll need 1 piece of media from the Meyer DVD:


  • Follow the instructions in the Multipart Track tutorial (on page 511 from Chapter 30)
  • Make a 4x3 DV-sized comp to place the in
  • Look at the video. The goal is to create three different elements, which will be tracked along with the camera movement. The first element will appear in the green area underneath the hi-hat. (Create some text or other element to go there.) It will follow/track the hi-hat as it moves up, out of the frame. Another element will track up, along with and over the white drum head. (Create another text block or element, using the white drum head as a background.) The third element will track down, again in the green space following the camera move. These elements could be text, or anything else you want.
  • Make a null layer to apply the track to.
  • Track the movement of the LS_hihat_snare video. (The trick is to hold the "option" key to move the search and track square to another part of the video as needed.)
  • Only use the Y (up and down) axis before applying to the Null layer
  • Use the Smoother (Found under the "Window" menu to smooth out the bumps a bit.
  • Make 2 separate elements to tie to the motion (1 for the camera tilting down, the other for the camera tilting up)
  • Parent these to the Null layer
  • Adjust for a pleasing look
  • When you are finished, render out a full-size (H.264) version in your week 12 folder.
  • Make sure it's called "multipart"

Thursday ---------------------------------------------------------------------------

Keying in AE

There are some bluescreen files you can use in this 70 MB zip file:

  • Blue Dance
  • blue
  • PM_Alex.tif

Or you can download the Shia LaBeouf video or perhaps Jean Claude Van Damme.

After Effects has some excellent built-in keying tools- but the footage should be lit well and recorded into a codec with good color space.

Most HD video codecs are fine to use for chroma keying- but some codecs have more color information than others (4:1:1, 4:2:2). It's important that the background is evenly lit. Note the different codecs in Blue Dance (DV) and blue (Animation).

Setting up your clips

Place your chromakey footage above the background. You will use the keying tools to remove the background to reveal the layer underneath.

After applying a key, it's often necessary to add a Matte Choker to fine-tune the edges.

Garbage matte (aka junk matte) - Often when subjects are shot for chroma keying, there are areas not masked or covered by the blue or green screen material or paint. These are typically outside of the subject's area of motion. Because they aren't the uniform blue or green required for color keying, we use what's called a garbage matte to get rid of them. In AE it's easy to use the pen tool to make a mask that serves as a garbage matte.

Color Difference Key

This key isn't the most intuitive keyer to use- but most of the good ones are like this. It has an additive eyedropper tool that allows you to easily create a good matte. It might be overwhelming for those new to keying. Link to Adobe article & a Lynda tutorial on the Color Difference Key.

Color Key

This is the basic color keyer in AE. It can work well if the footage was created in a 3D program with a highly uniform color background. While it works well with really uniform color keying, it's hard to get some bluescreen footage to work, as it's not extremely uniform. A little edge feather can conceal bad footage or lighting but will lose the fine details.

Linear Color Key

This is a more sophisticated and easy to use color keyer with the interesting feature: you can use the + eyedropper tool to add to your matte or the - eyedropper tool to subtract multple times.


The matte choler and simple choker let you modify the matte created by the key. This is a quick and dirty way to eliminate the fringing

Color Range

This is frequently used for video work. It is simple to use and has additive and subtractive eyedropper tools.

Difference Matte

A difference matte compares one layer to another and then keys out the info that's "different." This is usually used with footage shot from stationary cameras, or from motion controlled (repeatable) rigs. Imagine you have two layers, one is a static shot of a room. Another layer has the same shot, but a subject walks in. Using a Difference Matte, we can key out the subject.


This is an excellent keyer provided with AE and the one I recommend using for most video work. Check out the links below for additional tutorials on how to use it and make better mattes.

Key Cleaner

There's a good tutorial from Brian Maffitt on how to clean up nasty chroma key footage.

General tips:

Any good keyer will allow you to examine the matte. Ideally you want to adjust the settings until you get only black and white (what's keyed out and what remains visible).

Note that with all of the keyers, you will likely need to add an effect to get rid of an unwanted color fringe. The maniuplating the Hue / Saturation helps. You can use AE's spill supresser and the simple choker to clean up nasty edges.

Additional Keying Help & tutorials:

In-class Exercise

There are several bluescreen clips listed above. Use the keying tools and the info in the tutorial to put any of these clips together against any background you choose. (E.g. you could have the dancers dancing on the moon.) Can you add a shadow to make it more realistic?

Turn in a full-sized, square pixel movie (H.264) into the appropriate Week 12 Canvas assignment (bluescreen).



  • Read & work through Meyer, Chapter 32 (Shape Layers)
  • Make a 15 or 30 second fake (or real) ad or PSA. It must have:
    • audio
    • good graphic design
    • a layer that is obviously motion tracked to a video layer
    • Turn in a square pixel H.264 version.
    • Be sure to note what you did and how you carried out the motion tracking in the accompanying critique form.
  • Final Project script/storyboard

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